It may be useful, in a variety of settings, to utilize both a traditional engine (e.g., an internal combustion engine) and one or more continuously variable power sources (e.g., an electric motor/generator or hydraulic motor/pump, and so on) to provide useful power. For example, a portion of engine power may be diverted to drive a first continuously variable power source (“CVP”) (e.g., a first electric motor/generator acting as a generator, a first hydrostatic or hydrodynamic motor/pump acting as a pump, and so on), which may in turn drive a second CVP (e.g., a second electric motor/generator acting as a motor using electrical power from the first electric motor/generator, a second hydrostatic or hydrodynamic motor/pump acting as a motor using the hydraulic power from the first hydrostatic or hydrodynamic motor/pump, and so on).
In certain applications, power from both types of power sources (i.e., an engine and a CVP) may be combined for delivery of useful power (e.g., to drive a vehicle axle) via an infinitely variable transmission (“IVT”) or continuously variable transmission (“CVT”). This may be referred to as “split-mode” or “split-path mode” because power transmission may be split between a direct mechanical path from the engine and an infinitely/continuously variable path through one or more CVPs. In other applications, in contrast, useful power may be provided by a CVP but not by the engine (except to the extent the engine drives the CVP). This may be referred to as “CVP-only mode.” Finally, in still other applications, useful power may be provided by the engine (e.g., via various mechanical transmission elements, such as shafts and gears), but not by a CVP. This may be referred to as “mechanical-path mode.” It will be understood that torque converters and various similar devices may sometimes be used in the mechanical-path mode. In this light, a mechanical-path mode may be viewed simply as a power transmission mode in which the engine, but not the CVPs, provides useful power to a particular power sink.